Wide band electromagnetic horn antenna



Oct. 6, 1942. M. KATZIN 2,297,896

WIDE BAND ELECTROMAGNETIC HORN ANTENNA Filed March a, 1941' CONNECT/ON T0 CONNECT/0N T0 ANTENNA Z3 ANTENNA "24 Fly. .2

- 2-; 7'0 RECEIVER F119. 3

450 460 470 480 490 500 510 520 530 540 550 FREQUENCY IN MC/S INVENTOR.

MART/N KATZ/N ATTORNEY Patented Oct. 6, 1942 UNITE-D ES PATENT OFF-ICE 2,297,896 WIDEBENDFLECTROMAGNETIOlIbBN ANTENNA Martin Katalin, Riverliead, N. Y., *assigno'r to Radio Corporation of America, a corpdration of Delaware Application 'Mar ch a, 1941, Serial 1%.382-{2'91 1 Claim.

The present invention lelatestb tuna-short wave-radiators and, particularly,to radiators of the directive h'orn type. p

An'o'bject of the 'preserit' i'nvention is the immovement of the flqllilfl y Charaliteristic's of "short wave antennas generally.

Another object of th'e'prsent invention is the "provision of an-antenna system operative over a relatively wide frequency band with'minimum reflection.

Still another object is the improvement of the directivity and the simultaneous decrease of selectivity of horn antennas.

The above mentioned objects, and others which may appear from the following detailed description, are attained by utilizing a pair of horn radiators directed in the desired direction of directivity. One of the horns is so arranged with respect to the other that energy arriving thereat lags the energy arriving at the other antenna by an odd multiple of a quarter wavelength. The transmission lines connecting the horns to receiving equipment have such a differential in length that the energy applied to the receiver from the two horns is again in an additive phase relationship. That is, the difference in length of the transmission lines from the antennas to a common connection point is an odd multiple of a quarter wavelength.

The present invention will be more fully understood by reference to the following detailed description which is accompanied by a drawing in which Figure 1 illustrates in plan view a pair of horn radiators arranged according to the principles of my invention, while Figure 2 illustrates in cross-section the details of the transmission line connecting the antennas of Figur 1 together and to a receiver or transmitter, while Figure 3 is a family of curves illustrating the improvement in frequency band coverage obtained by utilizing the principles of the present invention.

In Figure 1, reference numerals l and 2 indicate a pair of directive horn antennas having their mouths l and directed in the direction of the desired maximum response, as indicated by the arrows R. Horns l, 2 are shown as protruding slightly through windows in the wall W of a building. To the throat ends II and I2 of the horns are connected resonant chambers 2| and 22 within which are located antennas 23 and 24. A transmission line bridle connects the two antennas 23 and 24 together in parallel and the continuation to a transmission line 26 to which is connected the receiver to be energized by-sigrials Picked up-by theantenna. The point '0f"6nhe6tion (if-transmission line 26 to bridle 25 is determined by considerations which will hereafter be described with reference to Figure -2.

Energy arriving-at horn 2 "lags that-arriving at-horn I by-the distance (1, "giving a phase displacement between the output-signals, assuming both horns to have identical electrical characteristics, of

360-g= 360---sin 0 where S is the center to center spacing of the horns and 0 is the angle between the wall of the building shown in Figure 1 and the plane at right angles to the direction of the signal. In a typical case the distance d amounted to 1.23). at midband frequency which, it will be seen, is very close to an odd multiple of a quarter wavelength. In connecting the horns in parallel an impedance matching bridle 25 was used which is shown in more detail in Figure 2. The bridle comprises a concentric transmission line having an outer shell 21 and an inner conductor 28. The inner conductor 28 is connected at each end to antennas 23 and 24 while the outer shell is connected to the casing of chambers 2| and 22. Since the energy applied to the conductor 28, at its two ends, from antennas 23 and 24 is not in an in-phase relationship, the output from the bridle is not connected to the center line CL, but is spaced to one side thereof a distance L which imposes a phase lag to the signals from antenna 23 identical to that experienced by the signals picked up by antenna 24. Distance L is therefore equal to 11/22 where v is the velocity of the waves along bridle 25 compared to that in free space. In this way, the phases of the two outputs are made equal at the point where the transmission line 26 is connected to the bridle. The transmission line 26 has therein a tapered line impedanc matching section. The inner conductor 29 is gradually tapered from a large diameter at its point of connection to conductor 28 to a smaller diameter at the other end. The purpose of this tapering of a portion of the connection line 26 is to transform the impedance of the transmission line 26 to a value equal to a half of the characteristic impedance of the bridle 25. Viewed from transmission line 26 the bridle 25 appears as two lines in parallel.

In an embodiment of the invention as constructed the bridle 25 had a surge impedance of ohms and the impedance of transmission line for no reflection should have been 37% ohms for perfect matching without transformation. However, since it was desired to use the same type of transmission line throughout the tapered line section 29 was used to transform the impedance of the single line to the proper value for direct connection to the bridle 25.

In Figure 3, curve A indicates the frequency response of a single one of the horn structures l or 2 in terms of percent reflection at the horn plotted against the frequency applied to the horn. A reflection of less than 10 percent is indicated over a frequency band from 472 to 522 megacycles. Curve B shows the measured characteristic of the parallel combination of .both horns with a phase quadrature displacement of the The principle discussed above may be used to advantage generally, where wide frequency bands are desired. The desired phase displacement of an odd number of quarter wavelengths may be obtained by adjusting the distance d. A choice of dimension such as d: \/4 gives the greatest increase of band width.

In accordance with the principles of my invention, where a number of horns which is an even multiple of two is used it is contemplated that they may be grouped in pairs as described with reference to Figure 1, and the pairs connected by bridles similar to those shown in Figure 2, with the pairs of horns so spaced that compensation is obtained for the phase quadrature connection of the bridles.

While I have particularly shown and. described several modifications of my invention, it is to be distinctly understood that my invention is not limited thereto but that improvements within the scope of the invention may be made.

I claim:

An antenna system comprising a pair of elongated horn antennae arranged side by side and having their longitudinal axes arranged in the same direction, said antennae being spaced along the direction of arrival of signals, one from the other, a distance equal to an odd multiple, including unity, of a quarter of the operating wavelength, a transmission line connecting said antennae together, and a transducer connected to said transmission line at such point along said line that phase shift caused by said spacing is compensated. I

MARTIN KATZIN. 

